U.S. Pat. No. 3,864,473 (1975) reveals substantive sunscreen polymer based on polyethyleneimine and p-N,N-dimethylaminobenzoic acid. U.S. Pat. No. 4,004,074 (1977) provides substantive polymeric sunscreen agents comprising an UV-absorbing moiety selected from salicylates, aminobenzoates and carboxy succinates and a substrate linking moiety selected from the group consisting of thiocarboxylic acids, mercaptans, guanidines and biguanidines.
U.S. Pat. No. 4,233,430 (1980) discloses an antisolar acrylamide backbone polymer containing coumarins, benzothiazoles, 3-(acrylamidomethylbenzylidine) DL camphor as sunscreen moieties. The water insoluble polymers of this invention are used in leave-on applications like antisolar lotion, cream, aerosol and oil. U.S. Pat. No. 4,524,061 (1985) teaches the art of making polymeric sunscreen agents that comprise of olefinic p-aminobenzoate, N-vinylpyrrolidinone, a vinyl lactam and acrylic or methacrylic acid. The polymeric sunscreens are claimed to have good adhesion to skin and to resist removal by salt or plain water. They are claimed to form a thin film that is easily removable by mildly alkaline soap or shampoo.
Interestingly, U.S. Pat. No. 5,204,090 (1993) discloses use of combination of water insoluble film forming acrylic polymer and sunscreen agents to yield water proof high SPF compositions. U.S. Pat. No. 4,508,882 (1985) employs UV-absorbing benzotriazole having vinyl group to make homopolymers as well as copolymers that are most effectively used for UV protection of plastics and wood. U.S. Pat. No. 5,063,048 (1991) discloses UV light absorbing skin-protecting composition based on acrylic polymeric backbone containing salicylates, benzophenones and benzotriazoles as sunscreen moieties.
It is pertinent to mention here that all the polymeric sunscreens reported so far have been water-insoluble. It was in 1992–93, U.S. Pat. No. 5,134,223 (1992), U.S. Pat. No. 5,243,021 (1993), U.S. Pat. No. 5,250,652 (1993) disclosed novel, water dispersible copolymers that contain UV-absorbing monomers based on moieties such as aminobenzoates and hydrophilicity was introduced by polyethylene glycol backbone.
Polymer bound 2-(2-hydroxyphenyl)2H-benzotriazole as UV absorber is disclosed by U.S. Pat. No. 5,099,027 (1992) for any exterior coating application (as in manufacture of optical lenses) and as components for sunscreening and suntanning lotions.
On the similar lines U.S. Pat. No. 5,487,885 (1996) and U.S. Pat. No. 5,741,924 (1998) provide acrylic polymers with UV absorbing moieties having different ranges in conjugation with another hydrophilic monomer. The polymers are insoluble in water but reported to swell in water and are meant for dermatological formulation that can be coated, sprayed, spread on the surface and are claimed not to unduly penetrate the dermal layer. Use of such polymers in coating of lens surface and in other opthalmological solutions is described. The UV absorbing moieties cover derivatives of dibenzoyl methanes, dimethylamino benzoates and phenyl benzamides.
From above discussion it is clear that a polymeric sunscreens of prior art are substantive by virtue of their film forming nature. Only exception is U.S. Pat. No. 4,004,074 (1977) where substantivity to skin was achieved through substrate linking groups like thiocarboxylic acids and mercaptans, etc.
Most of the UV-absorbing polymers reported so far are water-insoluble. To make these polymers useful for personal care products they need to be formulated with hydrophobic bases that give greasy feel. The water-insoluble polymers can be applied by aerosol spray preparations. However, the water-resistant films they form are quite difficult to remove. Hence there is a need to synthesise polymeric sunscreens that are water-soluble yet water-resistant once they are applied to skin, hair or fabric.
This is achieved in the present invention by synthesising water-soluble polymers containing cinnamidoalkylamines and/or benzamidoalkylamines that (a) have lower critical solution temperature (LCST) of 30° C. or above and (b) cationic centres for enhanced substantivity. When these water-soluble polymers are applied to skin, the temperature of body as well as the temperature of surroundling and the salt content of water (in case of swimming in the sea) make them insoluble and hence do not get easily washed off either by sweat or sea water. However, they can be easily removed by plain water (without salt) at ambient temperature (25° C.). These UV-absorbing polymers show excellent substantivity to hair as a result of cationic centres.
The main object of the present invention is to synthesise water-soluble macromolecules with cinnamido and benzamido moieties to provide UV-absorption and to provide significant levels of substantivity especially during an activity like swimming. Another object of the present invention is to prepare useful cosmetic formulations and formulations for fabric care employing these new UV-absorbing macromolecules.